Sensitization detection of aluminum alloy plates using laser-generated longitudinal waves

Sensitization refers to the formation of magnesium precipitates at the grain boundaries when Al-Mg alloy is exposed to elevated temperatures for extended periods of time, which can lead to reduced corrosion resistance and increased susceptibility to stress corrosion cracking. Since sensitization occurs at the microstructure level, a measurement technique that can measure multiple locations rapidly and is highly sensitive to minute changes is called for. This paper explores laser-generated longitudinal ultrasonic guided waves for sensitization detection in aluminum alloy plates. The samples were heat-treated to induce sensitization, and the degree of sensitization was determined by the nitric acid mass loss tests. The longitudinal ultrasonic guided waves were generated using a high-power pulsed free-space laser and detected using a continuous fiber laser. A digital signal processing algorithm has been developed to analyze the time-frequency components of the acquired signal. The experimental results demonstrated that the state of sensitization can be characterized by ultrasound parameters, such as attenuation.